This investigation is organized around a search for differences between normal human cells and their malignant counterparts in their basic growth requirements, and in the regulation of their entry into the cell cycle. During the past year, data have been gathered for normal human keratinocytes and a squamous cell carcinoma line that appear to demonstrate that malignancy has little effect on qualitative or quantitative requirements for most common nutrients that do not also have separate regulatory roles. We are now focusing more attention on regulatory growth factors and the small subset of nutrients whose quantitative requirements do appear to be affected by malignancy. We are also beginning to work with other types of human cells that frequently become malignant, including mammary epithelial cells and melanocytes, in order to determine whether our initial observations are valid for diverse cell types or only for keratinocytes. We are also beginning to turn our attention to mechanisms responsible for entry into the cell cycle of the various cell types that we will be studying. The defined media that have been developed for normal human epithelial cells will be used to determine whether entry of these cells into the cell cycle is governed by mechanisms similar to those observed with more widely studied fibroblastic cells. Specific models based on data from fibroblasts that will be tested for relevance to normal human epithelial cells include the concept of a stable and reversible G1(G0) arrest, the transition probability model, and the competence-progression model. Although these models are derived from cell types that rarely become malignant, they are currently widely used as starting points for the planning of experiments on the nature of malignant transformation. It is therefore of major importance to determine whether they are valid for cells of the types that most frequently become malignant in vivo. (N)